The present invention relates to a light transmitting plate member for illuminated signs, illuminated tables or similar illuminated flat items.
A light transmitting plate member 4 illuminated signs, illuminated tables or a similar illuminated flat item and adapted for uniform diffusion of light from a light source positioned at a side edge of the light transmitter which has a preferably flat side and an opposing side which has a gradual slope has been proposed wherein the plate member has a reduced thickness in a direction away from the first side edge, with opposite sides being provided with optically smooth surfaces as the light transmitting plate member includes transparent and light transparent material with specific optical properties.
A light transmitter or light source of the aforementioned type is described in, for example known from the description to Danish Patent Application 3800/84 and U.S. Pat. No. 3,464,133 relating to a display apparatus comprising a number of successively activated light sources, with the apparatus being adapted to animate a multi-dimensional picture when observed from the front side of a prismatic light transmitter being illuminated from a narrow side edge by one or more light sources.
These known devices and the light transmitting plate member according to the invention are based on the particular optical and/or light technical conditions in which a ray of light, introduced from a side edge of a prismatic member, is reflected from opposite surfaces of the member with a still reduced angle of refraction for each reflection is reduced with the cone angle of the prism, i.e. the angle of inclination between the opposite surfaces of the prism. By introducing not only a single ray of light but a pencil of rays of light under different angles of incidence into the light transmitter, a rather uniform diffusion of the reflected and finally transmitted rays of light from the light transmitter is obtained. As a matter of fact there is also applied a lower critical angle of refraction as well as an upper critical angle of refraction determined by the index of refraction for the actual material from which the light transmitting plate member is produced.
The invention has for its purpose to provide an improved light transmitting plate member of the aforementioned type by which, by simple measures, may be obtained a considerably better and uniform diffusion of light, with light transmitting plate members having a considerable length.
According to the invention the light transmitting plate member is characterized by the side with the gradual slope being provided with a number of angled divisions which are defined by transverse divisional lines which, in general, run parallel to the first side edge and which are positioned with either uniform intervals or with graded intervals which are reduced in the direction receeding from the first side edge. A height or the thickness of the light transmitting plate member at the transverse divisional lines, in general, corresponds to the thickness of the light transmitting plate member at the first side edge, whose angled divisions from the divisional lines and in the direction away from the first side edge have reduced thicknesses, i.e. are inclined in relation to a reference plane parallel to the first particular plane side of the light transmitting plate member. Hereby is obtained a quite new and improved type of light transmitting plate member which may be produced with a considerably less self-weight per unit of length and which is suitable for production by extruding, whereby also the costs of production may be minimized, of course on condition of a reasonably large production. Furthermore, the light transmitting plate member according to the invention shows a considerably increased efficiency as to uniform light diffusion ability, even with a rather considerable total length. By way of example the light transmitting plate member according to the invention may be produced from a rather cheap acrylic plate, e.g. having an initial thickness of about 10 mm and with a length of up to about 1400 mm and a width which nearly alone is determined by the width of the item which is to be illuminated, and of course, the actual used light source i.e. the length of, by way of example, a low voltage tube lamp (PL-lamp).
Preferably, the angles of inclination of the angled divisions of the opposite side and the mutual lengths between the divisional lines are varied in such a manner that each of the angled divisions or gradual slopes are illuminated approximately uniform by light diffusion from the the respective sides of the light transmitting plate member, of which the the first preferable plane side is considered as the front side of the light transmitting plate member which is preferably turned against the item which is to be illuminated e.g. a sign plate, while the opposite side of the light transmitting plate member with the gradual slopes is considered as the rear side of the light transmitting plate member whereby preferably a reflector is positioned being adapted to reflect the light right through the light transmitting plate member, i.e. out through the plane front side thereof.
Appropriately, the light transmitting plate member is produced from a preferably plane acrylic plate of minor thickness, e.g., 5-15 mm, preferably 10 mm and with a considerable length, e.g. 200-1400 mm, preferably about 1200 mm, as the angled divisions are varying from about 0.1.degree.-5.degree. nearest at the first side edge to about 5.degree.-20.degree. farthest of from the first side edge, in dependence upon the total length of the light transmitting plate member.